The present invention relates to route guidance in the context of a vehicle navigation system. More specifically, methods and apparatus are provided by which audible route guidance instructions are provided to the user of a vehicle navigation system.
The utility of providing voice guidance in vehicle navigation systems is unquestioned in the industry. This is particularly true where voice guidance reduces the necessity that the driver make visual contact with the system's display in situations where it may be hazardous to do so, i.e., when the vehicle is in motion. In fact, as speech synthesis and voice recognition technologies mature it is likely that vehicle navigation systems will become increasingly dependent on such technologies for many system functions including, for example, destination selection, route guidance, and even vehicle security.
Most currently available vehicle navigation systems provide some level of voice guidance to the user. For example, a driver might be alerted to an upcoming maneuver with a warning "Right turn ahead" or "Next exit on the left" when the vehicle is determined to be within some threshold distance to the maneuver. However, given the complexity and uniqueness of each vehicle's circumstances and the wide variety of road topologies, it is currently very difficult to provide voice instructions which describe an upcoming maneuver with even a moderate level of precision. That is, for example, systems do not typically identify the road at which the right turn is to be made or the name of the upcoming exit. This is largely due to the fact that vehicle navigation systems typically employ a library of voice instructions, the size of which is kept relatively small to conserve memory and processing resources. Obviously, recording and storing a number of maneuvers for each street name in a typical map database is not practicable.
It is therefore desirable to develop enhancements to current voice guidance techniques which provide a greater level of detail with regard to upcoming maneuvers without degrading overall system performance. It is also desirable that systems employing voice guidance techniques provide features which will enable the user to most effectively use the system. For example, presenting maneuver instructions only as the vehicle approaches the associated maneuver may not be sufficient to provide a desirable level of comfort for some users. Therefore, providing some means of previewing, reviewing, and/or repeating instructions is desirable. Another problem which needs to be addressed is the often dramatic variation in background noise affecting the user's ability to hear the instructions as they are given. Some means of compensating for this is therefore desirable.